This invention relates to storing digital information on a storage medium.
In some known optical storage schemes, a laser beam records the value of a digital bit either by ablating or not ablating a pit in a polymer film. The film may be part of a disk which is rotated relative to a recording head that includes the laser. A stream of bits may then be recorded along each one of successive circular tracks by modulating the laser beam (in accordance with the bit stream) in coordination with the rotation of the disk and with movement of the recording head relative to the disk. The difference in the optical characteristics of the ablated pit compared with a nonablated region enables the stored bits to be read optically by any one of a variety of techniques. Such a recording scheme may be capable of very high density storage, e.g., 10.sup.8 bits per cm.sup.2 or more.
Typically the disk is assembled of multiple layers, one of which absorbs laser beam energy sufficiently to become ablated. That layer may be sandwiched between other layers that provide mechanical strength and certain optical properties. For example an under layer may be reflective, while an over layer may be antireflective, thus enabling reading the bits using a laser beam. Reflection of the beam indicates an ablated pit; no reflection indicates that the beam has been absorbed in a non-ablated region.
In some schemes, the laser sensitive layer has a low melting point and the bit is recorded by melting a tiny spot of that layer. The layer may include a dye that specifically absorbs light at the frequency of the recording layer. Alternatively, a thermoplastic layer may be deformed rather than ablated. Photosensitive layers similar to photographic film have also been used.